• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.50-57
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• 2004

For the application of structural health monitoring such as AE detection, a stabilized FBG sensor system with wide dynamic range was proposed. A tunable Fabry-Perot filter with narrow free spectral range(FSR) was used to simplify the multiplexing demodulator for FBG vibration sensors. Stabilization controlling system was also developed for the maintenance of maximum sensitivity of the sensors. In order to verify the performance of the proposed FBG vibration sensor system, we measured sensitivity, and the system showed the average sensitivity of 256 $n{\in}_{mas}/{\sqrt{Hz}}$. Finally, multi-points vibration tests using in-line FBG sensors were conducted to validate the multiplexing performance of the FBG system.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.289-289
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• 2010

나노섬유는 지름이 수십에서 수백 나노미터(1나노미터=10억분의1m)에 불과한 초극세 물질로 비표면적이 매우 크고[1], 제작이 간편하여, 사용되어지는 고분자의 종류에 따라 에너지 환경 의료 관련 분야에서 전극소재 필터재 피복재 인공 피부등 다양한 분야에서의 활용이 가능하여 전 세계적으로 연구개발이 활발하게 이루어지고 있다. 그러나 그 자체만으로 응용하기에는 그 기계적 전기적 특성의 한계 때문에 응용의 다양성에 제약을 받고 있다. 그러나 그 자체만으로 응용하기에는 그 기계적 열적 전기적 특성을 가진 탄소나노튜브를 첨가한 복합나노섬유에 의해 그 응용영역의 한계를 넓혀가고 있다.[2] 본 연구에서는 전도성 고분자인 polymethyl methacrylate (PMMA)에 multi-walled carbon nanotubes (MWCNTs)를 첨가한 복합나노섬유를 전기방사법(electrospinning method)을 통해서 제조하였다. [2~3] CNTs 첨가농도에 따른 제조된 복합나노섬유의 형상변화와 섬유내의 CNTs 배열상태를 각각 주사전자 현미경(scanning electron microscope: SEM)과 투과전자현미경(transmission electron microscope: TEM)을 이용하여 관찰하였다. 또한, 복합나노섬유의 광학 특성 변화를 CNTs 첨가농도에 따라서 FT-IR과 Raman spectroscopy등을 이용하여 조사하였으며, 나노섬유의 tensile strength의 측정을 통해 CNTs 함량에 따른 기계적 특성 변화를 분석하였다.

• Radiation Oncology Journal
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• v.11 no.1
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• pp.183-191
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• 1993

The homogeneous dose planning is one of the most important roles in radiation therapy. But, it is not easy to obtain a homogeneous dose to paranasal sinus region including the ethmoidal sinus with conventional irradiation techniques. In this experimental study, the authors tried to get a homogeneous dose at PNS region, but the nasal cartirage does not exceed the tolerance dose, with anterior-posterior beam and two both lateral wedged beams. Used three fields were shielded with full thickness of blocks to preserve the eye-balls and with blocks of one half value layer to create a homogeneous dose at the whole treatment volume. The dose computations are based on the three dimensonal structure with modified scatter contributions of partial shielders and attenuated beams in 6 MV photon beams. The dose distributions of mid-plane is examined with Kodak verification films and teflon-embedded TLD rod (1 mm diameter and 6 mm length) to confirm the computed dose. In our study, the whole PNS regions have shown within $85{\%}$ of the resultant isodose curves with relatively homogeneous dose distribution. The results of dose computation and measurements are agree well within $5{\%}$ uncertainties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.663-669
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• 2016

A terahertz asymmetric split-loop resonator (ASLR) was analyzed for use in high-sensitivity sensing applications. Its structural asymmetricity induces an asymmetric Fano resonance which has a high quality factor compared to the symmetric eigen-resonance. The variations of the resonant frequency, transmission coefficient, and quality factor of the ASLR in the eigen and Fano resonances are analyzed as a function of its structural asymmetricity. Also, the surface current densities on the ASLR in both resonances are calculated to analyze the main cause of the variations of its transmission characteristics. The surface current of the ASLR in the eigen resonance shows a dipole resonance, which increases the radiation loss and reduces the quality factor. On the other hand, the surface current of the ASLR in the Fano resonance shows a trapped or quadrupole mode which has a low radiation loss. Therefore, the ASLR operated in the Fano resonance has a high quality factor. Terahertz, high-performance filters and high sensitivity sensors can be developed based on our analysis results of the ASLR having a high quality factor. These high-performance devices based on terahertz metamaterials could increase the adoption of terahertz industrial applications.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.4
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• pp.311-318
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• 2010

U. S. NRC Regulation Guide 1.52 regulating ESF ACS in nuclear power plants has been revised to revision 3. To apply reduction of operability test time, allowance of alternative challenge agents for in-place leak test of HEPA filters, and upgrade of Methyl Iodide penetration acceptance criterion in activated carbon performance test suggested in Reg. Guide 1.52(Rev.3) on Yonggwang units 5 and 6 ESF ACSes, technical feasibility study was carried out with on-site experiments as well as experiments with a lab-scale model. It was confirmed that the moisture in the system returned to the level before the test in 1 or 4 days even though the moisture was removed during the operability test lasting more than 10 hours. Therefore, it is appropriate to perform monthly operability test in 15 minutes just long enough to check the operability of equipment. To change challenge material for in-place HEPA filter leak test, size of aerosol, production rate, and leak detection capability were compared for DOP and PAO. It was concluded that PAO can be substituted for DOP in nuclear power plants. The upgrade of Methyl Iodide penetration acceptance criterion from 0.175 % to 0.5 % in active carbon filter bed deeper than 4 inches was to conform to the change of activated carbon performance test method to ASTM D3803(1989). It was confirmed that Methyl Iodide penetration acceptance criterion of 0.5 % under $30^{\circ}C$, relative humidity 95 % condition was conservatively good enough for testing performance of active carbon insitu. The licence change of Yonggwang units 5 and 6 has been completed based on this study.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.114-114
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• 2018

탄소 재료는 뛰어난 물성에서 다양한 재료로의 응용이 기대되고 있다. 특히, 이종 원소 함유 카본 재료는 전기적 특성과 촉매성의 발현 등 새로운 기능을 카본 재료에 부여할 수 있어서 연료 전지, 에너지 저장, 태양 전지 등에의 응용이 기대되고 있다. 최근, 용액 중의 저온 플라즈마인 솔루션 플라즈마(solution plasma process)를 이용하여 벤젠 용액 등에서 탄소 재료 합성에 성공하였다. 그러나 기존의 연구에서는 솔루션 플라즈마 프로세스를 이용하여 합성한 이종원소 카본은 전도성이 낮아 이종원소의 함유량을 낮추는 고온의 열처리가 필요했다. 따라서 본 연구에서는 우수한 물리적 전기적 특성을 갖는 그래핀(graphene)과 같은 이종 원소 카본 나노시트(heteroatom carbon nanosheets)의 합성 및 메커니즘(mechanism)에 대해 검토하였다. 다양한 이종원소를 포함한 유기용매 안에 바이폴라 펄스 전원에 의한 전압을 두 텅스텐 전극 간에 인가하고, 솔루션 플라즈마를 생성하여 이종원소 카본 재료를 합성했다. 플라즈마 생성은 텅스텐 봉을 전극으로 사용하고 전압을 2.0 kV, 펄스 주파수를 200 kHz, 펄스 폭을 $1.0{\mu}s$, 전극 간 거리를 1.5 mm에서 일정하게 유지하며 200 mL 유기용매 중에서 방전시키는 것으로 재료를 합성했다. 플라즈마 방전 후, 필터을 이용하여 흡인 여과한 뒤 $200^{\circ}C$에서 1 시간 동안 건조 시켰다. 건조 후의 이종원소 카본의 물리적 특성을 원소 분석, X선 회절 법(XRD), 저항률 측정, 투과형 전자 현미경(TEM) 및 라만 분광법, 전자 현미경(SEM), X-선광전자분광기(XPS)등을 이용하여 카본의 형상 및 특성을 분석하였다. 그 결과 다양한 이종원소를 포함한 유기용매 중 2-pyrrolidone을 사용했을 때, 이종 원소 카본 나노시트를 합성하는데 성공하였다. 또한, 이 연구방법을 통해서 솔루션 플라즈마 프로세스를 통한 카본 나노시트 합성의 메커니즘을 규명하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.80.2-80.2
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• 2012

그라핀(graphene)은 탄소 원자의 2차원 육각형 $sp^2$ 결합체로서 탄소 나노구조체가 가지는 여러 가지 우수한 특성을 보유하면서 대면적 기판 위에서 소자구현 및 투명전극 등으로의 우수한 응용성 때문에 고품질 그라핀 제조와 물리적 특성, 소자응용에 관한 연구가 활발히 진행되고 있다. 최근 그라핀 제조를 위한 여러 가지 방법이 개발되고 있으나 화학적 박리법이 저비용으로 대량생산을 위해 가장 유리한 방법으로 주목을 받고 있다. 화학적 박리법은 벌크 그라파이트를 강한 산을 이용하여 산화시켜 형성된 산화 그라파이트(graphite oxide)을 열적으로 팽창시켜 박리하고 환원하여 그라핀으로 제조하는 것이다. 보통 열적팽창을 위해서 열처리 로를 사용하게 되는데, 본 연구에서는 박리를 보다 효율적으로 진행시키고 고품질의 그라핀을 얻기 위해 마이크로웨이브를 이용한 박리법을 적용하였다. 마이크로웨이브는 설비가 간단하고 매우 균일하게 열팽창을 시킬 수 있을 뿐만 아니라 대량생산에서도 유리할 것으로 기대하였다. 천연 그라파이트(99.9%, 평균입도 $200{\mu}m$)를 Hummer 방법에 따라 $H_2SO_4$와 $KMnO_4$를 사용하여 산화시키고 필터링 후 마이크로웨이브를 조사하였다. 이후 환원 처리를 거쳐 그라핀을 제조하였다. 라만스펙트럼 및 투과전자현미경으로 분석한 결과 우수한 품질의 그라핀이 형성되었음을 알 수 있었다. 그라핀의 두께 및 품질은 마이크로웨이브의 인가시간 및 반복 횟수가 증가함에 따라 크게 영향받는 것을 확인하였다. 본 발표에서는 마이크로웨이브를 사용한 산화 그라파이트 박리 및 그라핀 제조라는 새로운 시도와 주요변수에 따른 그라핀 특성에 관한 결과를 논의할 것이다.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.226-232
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• 1999

We have investigated the output power performance of a continuous-wave chromium-doped YAG laser ($Cr^{4+}$:YAG laser), pumped by a Nd: YAG laser. With an output coupler of 1% transmission, we obtained as much as 400 mW of the average output power at 1.450 ${\mu}{\textrm}{m}$. The power slope efficiency of 8%, when the gain medium was cooled to 2$0^{\circ}C$. We tuned the wavelength of the $Cr^{4+}$:YAG laser, at pump power of 6 W, by using birefringent filter. As a result, lasing wavelength was tuned from 1.399 ${\mu}{\textrm}{m}$ to 1.532 ${\mu}{\textrm}{m}$, with the maximum output power of 340 mW at 1.4903 ${\mu}{\textrm}{m}$ and the linewidth was 0.21 nm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.721-725
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• 2007

A fiber optic based weight sensor has fabricated using a fiber Bragg grating with a weight sensitive. The sensing concept exploits the inherent characteristics of the FBG and is based on the strain effect induced in the fiber Bragg grating through. A direct indication of the weight level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. A FBG behaves like a spectral filter which has inherent characteristics that render it very sensitive to strain and temperature. The sensing principle is also based on the strain effect induced in the FBG through the caused by the weight. The experimental setup used for the initial investigation to characterize the mass response of the sensor. The transmitted signal from the sensor was monitored using an optical spectrum analyzer with a resolution bandwidth of 0.4nm. In this paper, we presented the spectral characterization and shaping of FBG by scanning a mass element that affects a small grating fraction at a time, without permanent effects on the optical fiber when the various wavelength and strain is removed. That is, destruction when the optical fiber for weight is physically damaged.

• Tuberculosis and Respiratory Diseases
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• v.51 no.3
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• pp.211-223
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• 2001

Background : Rhinovirus infection of the airways results in increased permeability of the airway vascular endothelium with the influx of plasma proteins, including lipids such as LDL. In vitro studies on the effect of oxLDL on leukocytes has shown many pro inflammatory effects on multiple leukocytes. We hypothesized that oxLDL is one mechanism for recruiting granulocytes to the airways during a RV infection. Therefore, chemotaxis and transendothelial migration, in response to nLDL, was determined for these granulocytes. Methods : nLDL was oxidized with 5mM Cu2S04 for 20-24 hours. 3-5 105 cells were loaded into the Transwell filter while the chemotatic agonists were placed in the lower well for chemotaxis. Confluent monolayers on HPMEC were grown on Transwell filters for transendothelial migration. The filters were washed and eosinophils and neutrophils loaded on to the filter with the chemotatic agonist was were placed in the lower well. The wells were incubated for 3 hours. The number of migrating cells was counted on a hemocytometer. Results : OxLDL, but not nLDL, is chemotatic for eosinophils and neutrophils. The level of granulocytes chemotaxis was dependent on both the concentration of LDL and its degree of oxidation. OxLDL stimulates eosinophil and neutrophils migration across HPMEC monolayers (+/-IL-$1{\beta}$ preactivation) in a dose dependent manner. Conclusion : Increased vascular permeability during a RV infection may lead to the influx and oxidation of LDL. The resulting oxLDL. is one possible mechanism for the recruitment of neutrophils and eosinophils to the airway interstitial matrix. Once in the airways, granulocytes can further interact with oxLDL to promote airway inflammation.